In electrothermic slag smelting furnaces, electrodes are oriented vertically and pass through the top of the furnace and penetrate into the molten slag. The electrodes are provided with alternating electric current to heat the slag by resistance heating. Normally, three vertical electrodes are used in electrothermic slag smelting furnaces. In order to allow current to flow through the slag, the bottom lining of the furnace is electrically conductive and constitutes a zero point for the current. One example of such a furnace is disclosed in U.S. Pat. No. 6,440,193. This patent relates to a process and reactor for the carbothermic production of aluminum wherein a molten slag bath of alumina (Al2O3) and aluminum carbide (Al4C3) is produced in separate compartments.
It has been found that the use of the electrically conductive bottom lining in electrothermic smelting furnaces has a number of disadvantages. One of the disadvantages of the conductive bottom is that, because of the high wear on the bottom lining, the life of the bottom lining is reduced and repairs or replacements to the bottom lining are frequent. The high wear on the bottom lining is due to the high temperature to which the bottom lining is subjected because the bottom lining is the zero point for the current that flows through the slag of the furnace. Another major disadvantage to the conductive bottom lining is that when the furnace is shut down, restarting of the furnace is difficult due to the solidification or freeze-up of slag in the furnace during the shutdown. Accordingly, there remains a need for an electrothermic smelting furnace having an electrode arrangement substituting for the bottom lining as an electrical contact.